Trametes villosa laccase was used for direct azo dye degradation, and the reaction products that accumulated after 72 h of incubation were analyzed. Liquid chromatography-mass spectrometry (LC-MS) analysis showed the formation of phenolic compounds during the dye oxidation process as well as a large amount of polymerized products that retain azo group integrity. The amino-phenol reactions were also investigated by 13 C-nuclear magnetic resonance and LC-MS analysis, and the polymerization character of laccase was shown. This study highlights the fact that laccases polymerize the reaction products obtained during long-term batch decolorization processes with azo dyes. These polymerized products provide unacceptable color levels in effluents, limiting the application of laccases as bioremediation agents.The chemical structure of dyes is comprised of a conjugated system of double bonds and aromatic rings. The major classes of dyes have antroquinoid, indigoid, and azo aromatic structures. All of these structures allow strong -* transitions in the UV-visible (UV-Vis) area, with high extinction coefficients that allow us to consider these structures dye chromophores. Of all of these structures, the azo aromatic one is the most widespread dye class in the industry. The main drawback of this class of dyes is that they are not easily degraded by aerobic bacteria, and with the action of anaerobic or microaerobic reductive bacteria, they can form toxic and/or mutagenic compounds such as aromatic amines (9, 10, 34). There is a great environmental concern about the fate of these dyes, with special emphasis on reactive dyeing of cellulosic fibers, where large amounts of unbound dye are discharged in the effluent (24).Laccases have been extensively studied for their degradation of azo dyes (1,5,8,17,19,21,23,33). These enzymes are multicopper phenol oxidases that decolorize azo dyes through a highly nonspecific free radical mechanism forming phenolic compounds, thereby avoiding the formation of toxic aromatic amines (8,35). Over long periods of time, there can be a coupling between the reaction products, and even polymerization. It is known that laccases can catalyze the polymerization of various halogen-, alkyl-, and alkoxy-substituted anilines (15). In the literature, there is a large number of papers reporting on the decolorization of azo dyes; however, the fate of the products of azo dye laccase reactions and their possible polymerization have been ignored (7,16,25,28). Therefore, the purpose of this work was the study of azo dye degradation products in the presence of laccase. Direct azo dye laccase degradation and amino-phenol polymerization were performed for several days. The formed soluble products were studied by liquid chromatography-mass spectrometry (LC-MS), and the polymerized insoluble products were studied by 13 C-nuclear magnetic resonance ( 13 C-NMR). MATERIALS AND METHODSDyes, reagents, and enzymes. The investigated dyes, 3-(4-dimethylamino-1-phenylazo) benzenesulfonic acid (dye I) and 3-(2-hydroxy-1-naphthyl...

Power ultrasound of 850 kHz at 60, 90 and 120 W was used for the degradation of industrial azo dyes Acid Orange 5 and 52, Direct Blue 71, Reactive Black 5 and Reactive Orange 16 and 107. The results show that power ultrasound is able to mineralize azo dyes to non-toxic end products, which was confirmed by respiratory inhibition test of Pseudomonas putida. All investigated dyes have been decolorized and degraded within 3-15 h at 90 W and within 1-4 h at 120 W, respectively. Mass spectrometric investigations show, that hydroxyl radicals attack azo dyes by simultaneous azo bond scission, oxidation of nitrogen atoms and hydroxylation of aromatic ring structures. A volumetric scale-up showed a correlation between the energy input and the absolute amount of degraded dye. Up to an energy input of about 90 W no enzymatic deactivation of laccase was observed which might be helpful for a simultaneous action of sonochemical and enzymatic treatments.

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The goal of this work was to investigate the decomposition of azo dyes by oxidative methods, such as laccase and ultrasound treatments. Each of these methods has strong and feeble sides. The laccase treatment showed high decolorization rates but cannot degrade all investigated dyes (reactive dyes), and high anionic strength led to enzyme deactivation. Ultrasound treatment can decolorize all tested dyes after 3 h at a high energy input, and prolonged sonication leads to nontoxic ionic species, which was demonstrated by ion chromatography and toxicity assays. For the first time, it was shown that a combination of laccase and ultrasound treatments can have synergistic effects, which was shown by higher degradation rates. Bulk light absorption and ion-pairing high-performance liquid chromatography (IP-HPLC) were used for process monitoring, while with reversedphase HPLC, a lower number of intermediates than expected by IP-HPLC was found. Liquid chromatographymass spectrometry indicated that both acid orange dyes lead to a common end product due to laccase treatment. Acid Orange 52 is demethylated by laccase and ultrasound treatment. Further results confirmed that the main effect of ultrasound is based on˙OH attack on the dye molecules.

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Sixteen sulfonated and unsulfonated azo dyes as well as eleven sulfonated and unsulfonated aromatic amines were analyzed and qualitatively characterized by means of pyrolysis gas chromatography/mass spectrometry at different temperatures. Aniline and aminonaphthalene were found to be the dominant pyrolysis products of sulfonated aromatic amines and dyes. Azo dye and dye class specific key compounds such as benzidine, vinyl-p-base and 4-aminoazobenzene could be identified by pyrolysis gas chromatography/mass spectrometry of commercial acid, cationic, direct, reactive and solvent dyes. 500 degrees C was the optimal pyrolysis temperature for most of the pyrolyzed compounds. The method was applied to a dried sample of a textile wastewater concentrate from a dyeing process. Reactive azo dyes of the group of Remazol dyes and anthraquinone dyes could be identified as the major compounds of the sample. The finding of caprolactam (a printing additive) suggests that the wastewater contained effluent from a process of heat-activated printing with reactive dyes. p-Chloraniline, a banned aromatic amine, was identified. Chemical reduction of the wastewater sample prior to pyrolysis resulted in the release of volatile aromatic amines and aided the classification of several products of pyrolysis.

A biological high-performance treatment process comprising two 40-L reactor compartments has been developed for purification and decoloration of concentrated textile wastewater containing up to 15 g L(-1) reactive dyestuff. The decoloration rate of 95% meets the requirements of German legislation for textile wastewater treatment. Successful process development and optimization was achieved by use of high-performance liquid chromatography, with diode-array and electrospray tandem mass spectrometric (LC-ESI-MS-MS) detection, coupled with inline microfiltration membrane-sampling devices, applied online to bioreactors as a process analytical tool for the first time. The optimum process performance was found by correlation of dye and decoloration product-specific concentrations with summary properties such as redox potential and dissolved oxygen content. Details of the degradation and decoloration mechanism for the azo dye reactive black 5 was revealed by using mass spectrometry for structure elucidation.